Electrical switches - Page 2 - Fiberglass RV


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Old 12-01-2013, 07:00 PM   #15
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Electrical switches are UL compliant when they are installed and operated according to their UL listing.
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Old 12-01-2013, 08:19 PM   #16
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I wonder Robert, will Nest Caravans be a member of RVIA?
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Old 12-01-2013, 08:52 PM   #17
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Quote:
Originally Posted by steve dunham View Post
Electrical switches are UL compliant when they are installed and operated according to their UL listing.
UL is a private company, not a government listing company unlike the CSA which is a Canadian government.
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Old 12-01-2013, 09:00 PM   #18
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UL story.

I purchased an environmental chamber and had it installed. It required an electrical inspection before I could use it. The local government inspector came out looked over the chamber, while he was at it I pointed out the UL sticker on the computer that controlled the chamber. Since it was built in that was good enough for him and he signed it off. The chamber had purchased the computer complete with UL sticker but did all the rest of wiring themselves.
UL doesn't have much meaning.
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Old 12-01-2013, 09:09 PM   #19
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Maybe the inspector hadn't had lunch yet.

baglo
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Old 12-01-2013, 10:34 PM   #20
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Originally Posted by Glenn Baglo View Post
Maybe the inspector hadn't had lunch yet.

baglo

Maybe, I don't remember what time of day he came out.
This pretty common according the chamber manufacturer. I could have paid an extra $1500 to have the whole chamber UL certified before delivery. The recommended not because my experience is common.
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Old 12-02-2013, 09:41 AM   #21
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Okay, thanks for that.

Back to my question: can I use a switch rated for 24vdc in a 12vdc environment "legally"?
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Old 12-02-2013, 10:17 AM   #22
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If the switch is rated for 24 VDC. Is good for 12 VDC. The rating is a maximum. That being said. I would not exceed the 24 VDC current rating, unless it had a higher published 12 VDC rating.
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Old 12-02-2013, 10:32 AM   #23
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Quote:
Originally Posted by Byron Kinnaman View Post
Switches are rated by peak voltages, a 120 Volt AC switch is designed so that it voltage is which it will arc is well above peak voltage, with in this case is 1.4 x 120.
As far as zero crossing, zero crossing does occur in AC voltages, but a mechanical switch isn't going to always switch as zero crossing, any more than it will always switch a peak voltage. MYTH.

Current rating is determined by the size of the contacts, AC or DC matters not. A 20 amp contact is a 20 amp contact no matter the voltage.

I know the myths are because you read it on the internet.

The two PDF files linked to are concerning going from a low voltage switch to a higher voltage circuit. Going that direction is a problem, going from a higher rated switch to a lower voltage is not a problem.

Byron, I think you may want to rethink you statements. A DC arc is much more difficult to extinguish. The zero crossing I refer to is not necessarily going to occur when the switch is thrown, but it will occur no more then 1/120th of a second after. This makes breaking the current much easier. In a DC application that zero crossing never happens.

I especally take issue with:
Quote:
Originally Posted by Byron Kinnaman View Post
Current rating is determined by the size of the contacts, AC or DC matters not. A 20 amp contact is a 20 amp contact no matter the voltage.
I am happy that you contradict this statement in your last paragraph. I am assuming that you are referring to the ampacity of the contacts. Which would be true, but it is current breaking ability that matters. If you have a highly inductive load, at a higher then rated voltage, the switch may not be able to break the arc, and a fire may result. Why would they be rated for current, and voltage, if this was not significant?

In high voltage switch gear, in a substation, they use huge quantities of oil or some other pretty exotic techniques are used to extinguish an arc.

I think to OP should consult a codes expert before they get a bad name for cutting corners against best practices.
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Old 12-02-2013, 10:44 AM   #24
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Okay, thanks for that.

Back to my question: can I use a switch rated for 24vdc in a 12vdc environment "legally"?
I certainly think it's legal.
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Old 12-02-2013, 10:48 AM   #25
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David, I am confused with your final sentence of your second-to-last post. You write:
"I would not exceed the 24 VDC current rating, unless it had a higher published 12 VDC rating."
Can you elaborate?

Again, my goals in using low-volatage, DC-rated, 24VDC switches in my 12VDC environment are not only functionality and safety, but also legality.

Thanks again to all for your participation.
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Old 12-02-2013, 10:55 AM   #26
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I was just cautioning against thinking that at 12 VDC, instead of 24 VDC, it may have a higher current rating.
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Old 12-02-2013, 11:11 AM   #27
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Quote:
Originally Posted by David Tilston View Post
Byron, I think you may want to rethink you statements. A DC arc is much more difficult to extinguish. The zero crossing I refer to is not necessarily going to occur when the switch is thrown, but it will occur no more then 1/120th of a second after. This makes breaking the current much easier. In a DC application that zero crossing never happens.

I especally take issue with:


I am happy that you contradict this statement in your last paragraph. I am assuming that you are referring to the ampacity of the contacts. Which would be true, but it is current breaking ability that matters. If you have a highly inductive load, at a higher then rated voltage, the switch may not be able to break the arc, and a fire may result. Why would they be rated for current, and voltage, if this was not significant?

In high voltage switch gear, in a substation, they use huge quantities of oil or some other pretty exotic techniques are used to extinguish an arc.

I think to OP should consult a codes expert before they get a bad name for cutting corners against best practices.
Voltage and current ratings ==== Voltage rating is the highest voltage usable without the open switch arcing. Current rating is the highest current the contacts and conductors inside the switch can carry with heating up.

Arcing is going to happen, the ratings for cycles, that is on/off cycles, is a product of contact life or how long it will take to burn up the contacts.

Oil cooling it is used to keep the contacts cool so that more can be pushed through the contact than could in free air and has nothing to do with low voltage applications.

Switches are designed to open and close rapidly to reduce arcing and the time the contacts are in the arc zone.

Because the OP is concerned about low voltage operations with a resistive load I not going to go into all the switch design considerations of higher voltage switching. Nor will I go into different type contact material why different materials are used and when.

Also why you use reed switches or snap action switches, etc. For something that is seemingly simple there's a lot to it.

One more thing the arc is stopped by the spacing of the contacts. Since the maximum voltage in an AC circuit is 1.4 volts above the RMS (the voltage your meter reads) AC switches have to have a larger spacing between the open contacts.

You can believe what you like.
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Old 12-02-2013, 11:18 AM   #28
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Quote:
Originally Posted by Byron Kinnaman View Post
Oil cooling it is used to keep the contacts cool so that more can be pushed through the contact than could in free air and has nothing to do with low voltage applications.
As a former sub station designer, I can assure you that you are incorrect on this one. Large blade style disconnects are used, with no oil, they do not require cooling, but they are not able to interrupt the current, (I have a great story on this). The oil in a bulk oil breaker is not for cooling. That would be a transformer.

But as you said, nothing to do with low voltage.

But, there is a current and voltage rating for a reason.
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